Wind energy systems have gained more and more importance as a source of energy in recent years. As areas suitable for their economical operation are relatively scarce in a number of countries, a growing number of wind energy systems are located close to populated areas. As the operation of wind turbines in wind energy systems results in noise emissions, this leads to various problems such as resistance from neighborhoods and the like. A variety of factors contribute to the overall noise emission of such systems such as tonal noise emissions and aerodynamic noise emissions. In certain locations and regions, local ordinances or other regulations limit the allowable emission of noise.
During normal operation, wind turbines with sophisticated control systems maintain constant speed and power by active blade pitch control. In addition, wind turbines have a controller which adjusts the pitch angle of the blade to optimize energy captured below rated winds and regulates power above rated winds. The controller may utilize a fixed fine pitch angle in the variable speed region and adjust the pitch in above rated wind speed depending on the power output and rotational speed of the turbine.
Methods for reducing the noise emissions of wind energy systems have long been discussed. For example, it has been proposed to reduce aerodynamic noise caused by the blades through a speed/torque control of the system in order to keep turbine speed low during certain time intervals, e.g., during night time or other times in which reduced noise is desired. Such derating greatly reduces the power production. Another proposed method to reduce noise emission is to reduce rotor rotational speed of certain wind turbines in a wind park individually, also referred to as “derating” the wind turbine, in order to gain maximum overall performance of the system while meeting park noise constraints. Such selective derating of individual turbines permits a number of wind turbines to run at significantly higher speeds than the average speed of all the remaining turbines. This proposed solution provides greater power capture than a complete derating of the park, but provides reduced noise control and operation at reduced power coefficients.
It would be beneficial to provide a method and system in which the turbine can be controlled to extract a maximum or near maximum amount of power from the wind at a controlled noise level.